WooCommerce: Add Custom Field to Product Variations
WooCommerce Custom Fields: A Comprehensive Guide | WP Swings
GitHub - kharissulistiyo/WooCommerce-Custom-Product-Data-Fields: Simple framework which will help you to build extra product data fields, e.g. secondary product title, vendor info, custom message for individual product, etc.
WooCommerce Custom Fields for Variations - Plugin for WooComerce
How to add custom field in the general tab of Product - Webkul Blog